On Mon, Oct 03, 2022 at 01:26:23PM +0200, Ard Biesheuvel wrote:
> The ESRT code currently contains some sanity checks on the memory
> descriptor it obtains, but these can only trigger when the descriptor is
> invalid (if at all).
>
> So let's drop these checks, and instead, disregard descriptors entirely
> if the start address is misaligned, or the number of pages reaches
> beyond the end of the address space. Note that the memory map as a whole
> could still be inconsistent, i.e., multiple entries might cover the same
> area, or the address could be outside of the addressable VA space, but
> validating that goes beyond the scope of these helpers.
>
> Signed-off-by: Ard Biesheuvel <ardb@xxxxxxxxxx>
> ---
> drivers/firmware/efi/efi.c | 13 +++++++------
> drivers/firmware/efi/esrt.c | 18 +-----------------
> 2 files changed, 8 insertions(+), 23 deletions(-)
>
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index 11857af72859..55bd3f4aab28 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -461,19 +461,20 @@ int efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *out_md)
> efi_memory_desc_t *md;
>
> if (!efi_enabled(EFI_MEMMAP)) {
> - pr_err_once("EFI_MEMMAP is not enabled.\n");
> + pr_warn_once("EFI_MEMMAP is not enabled.\n");
> return -EINVAL;
> }
>
> - if (!out_md) {
> - pr_err_once("out_md is null.\n");
> - return -EINVAL;
> - }
> -
Nit: this seems unrelated.
> for_each_efi_memory_desc(md) {
> u64 size;
> u64 end;
>
> + /* skip bogus entries */
> + if ((md->phys_addr & (EFI_PAGE_SIZE - 1)) ||
> + (md->phys_addr > 0 &&
> + (md->num_pages > (U64_MAX - md->phys_addr + 1) >> EFI_PAGE_SHIFT)))
> + continue;
Should this also check if md->num_pages is 0? Also, should this check
be part of for_each_efi_memory_desc()?
> +
> size = md->num_pages << EFI_PAGE_SHIFT;
> end = md->phys_addr + size;
> if (phys_addr >= md->phys_addr && phys_addr < end) {
> diff --git a/drivers/firmware/efi/esrt.c b/drivers/firmware/efi/esrt.c
> index 2a2f52b017e7..8f86f2b0734b 100644
> --- a/drivers/firmware/efi/esrt.c
> +++ b/drivers/firmware/efi/esrt.c
> @@ -247,9 +247,6 @@ void __init efi_esrt_init(void)
> int rc;
> phys_addr_t end;
>
> - if (!efi_enabled(EFI_MEMMAP))
> - return;
> -
> pr_debug("esrt-init: loading.\n");
> if (!esrt_table_exists())
> return;
> @@ -263,21 +260,8 @@ void __init efi_esrt_init(void)
> return;
> }
>
> - max = efi_mem_desc_end(&md);
> - if (max < efi.esrt) {
> - pr_err("EFI memory descriptor is invalid. (esrt: %p max: %p)\n",
> - (void *)efi.esrt, (void *)max);
> - return;
> - }
> -
> + max = efi_mem_desc_end(&md) - efi.esrt;
> size = sizeof(*esrt);
> - max -= efi.esrt;
> -
> - if (max < size) {
> - pr_err("ESRT header doesn't fit on single memory map entry. (size: %zu max: %zu)\n",
> - size, max);
> - return;
> - }
This can still happen if the ESRT pointer is very very close to the end
of a memory map entry, unless there is another check that handles
such cases.
--
Sincerely,
Demi Marie Obenour (she/her/hers)
Invisible Things Lab
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